Central Connecticut's Kris Larsen isn't exactly your typical astrophysicist. Larsen is young and brash; listens to death metal bands; wears tattoos and an eyebrow ring. And then there's gender. Larsen is a she.

In the unspoken division of sciences into hard and soft - men's work and women's work - theoretical physics remains the ultimate male bastion. Larsen tells stories. The time as a grad student she went to hear a Nobel prizewinner lecture, and in the Q and A afterward he ignored her, then apologized by saying he assumed she was someone's girlfriend. Or the conferences she attended with her thesis adviser, UConn's Ronald Mallett, who is African American, another group scarcely represented among physicists. "You know that scene in `The Exorcist' when her head goes completely around?" Larsen recalls. "That's what happened whenever we two came in! People would just stare! It was like, `OK, they're lost!'"

In fact, science is how Larsen found herself. As a little girl in Hamden she was fascinated by dinosaurs - "the ultimate dinosaur geek," she calls herself. In middle school, paleontology gave way to chemistry, "until my little brother nearly blinded himself with my chemistry set, and my mother threw it out." Finally, Larsen discovered the mysteries of black holes and the stars. "At 16, I had it all planned out. I'd have my Ph.D. by 27, I'd get a job at a university, and that would be my life." She pauses. "I was off by six months on the Ph.D." Larsen says she can't imagine doing anything but teaching science. "Well, maybe being a roadie in a rock band. I can schlep equipment around."

And there goes another expectation: Whoever thought a physicist would be so funny? But Larsen is a hoot, both out of class and in. During her explanation of eruptive variable stars, someone in the domed lecture room in Copernicus Hall loudly sneezes. "That's it!" Larsen quips, not missing a beat. She describes a white dwarf, a collapsing star with a density of 1,000 tons per tablespoon, as "more dense than your average `Baywatch' star." And to illustrate the action of pulsars, she performs "the pulsar dance" - spinning around, arms angled out to represent magnetic poles, fingers waving to indicate beams of radiation shooting from the poles. The winner of last year's Excellence in Teaching Award at CCSU is whirling like a dervish at the front of the classroom, impersonating a rapidly rotating neutron star.

There's a method to this mirth. The cosmic speculations of Einstein and his heirs are dauntingly abstract. Light bent by gravity. Spherical space-time curving in on itself. An eternally expanding universe. Theoretical physics stands for everything that makes us feel intellectually puny. Most of Larsen's students are non-majors, and her lively classroom act - "it's vaudeville when I teach," she says - makes students more comfortable in an intimidating subject; her humor is a pedagogical strategy.

Larsen is "intuitively sensitive" to how overwhelmed students can feel, says Marty Connors, who has taken several courses with her. "She has an amazing knowledge of physics and astronomy, but she also has the ability to simplify the subject to help you get your arms around it. She doesn't hit you right up front with all the glorious complexities."

It's exciting to watch a gifted teacher deftly bring astronomy down to Earth. Larsen leads not with math, but with metaphor. She never stops comparing things to other things. The collapse of outer layers into the core of an exploding red super giant is like a bunch of Keystone cops piling into each other. Quasars are baby galaxies going through teething pains. Binary stars in asymmetrical mutual orbit are like Eric Cartman and Kenny riding a seesaw in "South Park." Lecturing on the collapse of a white dwarf, Larsen invokes a principle from quantum mechanics, the Pauli exclusion principle, that requires electrons to occupy only those energy states not already occupied by other electrons. She compares this to students entering a classroom, each taking an empty seat: "One person, one chair; one electron, one seat." Now, she says, imagine the room shrinking, collapsing like a star, the seats getting closer and closer together. "What would determine the limit to how far we could crunch this room down? It would stop when the chairs were as close as they could possibly be, right?" Well, same for the white dwarf, whose collapse is halted when its electrons are in danger of violating the Pauli exclusion principle. The technical name for this, Larsen tells the class, is degeneracy pressure. "But you should think, if the electrons were any closer together, they'd be sitting in each other's laps, and that's not allowed."

The profusion of analogies brings home the essential poetry of science teaching. In her big purple notebook Larsen keeps a Buddhist sage's advice to teachers, urging them to "abandon dispiritedness" and revel in "the hardships of explaining." She herself is a master explainer - a translator, really, shuttling endlessly between the highly mathematical language of theoretical physics and the everyday language of people like you and me. And her metaphors stick. A week later in Stellar Astronomy, she reviews the Pauli exclusion principle. "Oh yeah," says a student in the front row. "The musical chairs thing. When they can't get packed in any closer."

After class I ask where she gets her ideas. "I come up with a lot on the fly," she says. "If something works, I'll use it again. It's very improvisational." Of course, every analogy breaks down eventually, Larsen notes. "Sometimes students will really run with something, and I have to say, `Whoa, wait a minute, it isn't really like that!' You've got to weigh whether the analogy is worth the misconceptions that might go along with it." I'm struck yet again by how complicated teaching is - to find a graspable metaphor and then, even as you use it, to think about its limitations. Great teaching is expertise plus: You have to talk the subject while thinking the process.

Then again, multitasking is a way of life for Larsen. In a forty-minute break between Stellar Astronomy and Cosmology, she rushes back to her office, where she puts on a CD of Dream Theater's "Falling Into Infinity" and checks her e-mail - she'll get fifty in an hour sometimes, she tells me - while offering quick advice to a student who stops by with a physics problem. She fields a phone call from an administrator about another student who, according to the university's computer, doesn't exist. She briefs me on her crammed schedule. Tomorrow a group of prospective honors applicants to welcome at a breakfast. Saturday a Partners in Science workshop she's running for Hartford school kids. "I should learn to say no," she mutters, tearing through her pile of snail mail. A letter informs her she has been nominated to the union council. "Where are the hours supposed to come from?" she moans. "I barely have time to sleep!"

Larsen is a home-grown Central product; she graduated in its first honors program class in 1984, and her dedication to her alma mater and its students seems bottomless. In class, if someone can't find a handout from the last meeting, she makes a crack - "You got a quarter?" - then heads out to make a copy. In her jovial informality and her willingness to do almost anything for her students, Larsen seems like a born teacher, and she downplays her own accomplishments as a scientist. This is misleading. "Kris was a brilliant graduate student," says Ronald Mallett of UConn. "Her doctoral thesis advanced our understanding of the evolution of black holes and their connection to the structure of the universe." Larsen, Mallett says, faced a promising career as a researcher in astrophysics, but chose to focus on teaching instead. "Kris is a very, very gifted science teacher," he says. "She has the knack for making it exciting."

She makes it exciting because she finds it exciting. Whether she's advising a children's book author on star drawings; dissuading people who show up with rocks they're convinced are meteorites ("meteorwrongs," Larsen jokes); lecturing on the astronomy of Middle-Earth at a Tolkien convention in Germany ("I'm a major Tolkien geek," she confesses); or traveling to an annual stargazers party in Vermont ("200 people, 500 telescopes, and no indoor plumbing!"), Larsen clearly loves what she does. She still thrills to backyard astronomy - the excitement of "eyeball on glass," as she calls it, locating a faint galaxy she has never seen before, 60 million light-years away. "Kris always shows her sense of fun and curiosity," Marty Connors says. "She's an exceptionally engaging teacher."

Sitting through Larsen's classes - especially her advanced Cosmology class - means battling through numerous topics bewildering to me, with my lone, long-ago year of college math and physics. But beyond the bafflements of tensor calculus lies an ever-ready reach for the big picture. One day, toward the end of a Science and Society class in which Larsen has lectured on women astronomers at early 20th-century Harvard, a kid in a back row asks - out of the blue, as it were - "Do we have any idea, like, what shape our universe is?"

Larsen answers that the universe could have one of three shapes. She draws them on the board: flat; spherical or hyperbolic - a universe "like a Pringle's potato chip," she says. Which of these three is most likely depends on calculations of the amount of matter in the universe. And that, Larsen says, is very hard to do. Any other questions?

Hands fly up; somehow she has struck a speculative vein. Can we go faster than the speed of light? How old is the universe? What will happen when our sun dies? A student asks how many galaxies there are in the universe, and Larsen answers with a dead-on Carl Sagan impersonation: "Billions and billions." Later she'll joke about it, how every class at some point in the semester comes out with what she calls "the big, Jungian questions." But it's clear she's enjoying it. After all, the origins of the universe and the mystery of our ultimate fate - these are the questions that got Larsen hooked in the first place. And we want that from the Great Professor. Do the details, but do the big Jungian stuff, too.

On my last day at Central, another exchange between Larsen and a student sums up something else I've seen from all three professors whose classes I've visited. In Stellar Astronomy, Larsen has just finished doing her funky little pulsar dance when a student asks, What makes a pulsar spin so fast, anyway?

Larsen pauses, only partly to catch her breath. "Ten years ago I would have said, conservation of angular momentum." She explains the concept by referring to a spinning skater who draws her arms in to speed up - like a star whose mass is collapsing, making it spin faster. "But by now we've observed too many that don't behave this way. So now we have to say, `I dunno.'" She shrugs. "It's one of those areas of knowledge that is evolving."

The response focuses for me just how much is required of those few professors who make our list of all-time greats. Not only the commitment to excellence in every interaction. Not only the well-built lecture and the brilliantly conducted seminar. Not only the vision to see the universe in a building's design, or a soldier's memoir, or a Pringle potato chip, and not only the depth of knowledge that makes him or her a walking, breathing archive in their field. There's something more paradoxical that the Great Professor does for us - namely, to convey the thrill of what he or she doesn't know. It's one of those areas of knowledge that is evolving. The Great Professor insists that our facts, our ideas, our conclusions, even our systems of knowledge themselves are provisional. He or she reminds us how thrilling it is to venture beyond what we know; and in so doing, equips us for a lifetime of taking on new challenges.

It's a truism, I suppose, but what makes education so inescapably hopeful is precisely this zest for the unknown. Great professors convert not-knowing from an embarrassment to an excitement, and show us how to turn our quandaries into opportunities. That is why we keep drawing on them all our lives. At the end of the Big Jungian Questions class, a student asks Larsen whether it might be possible to travel faster than the speed of light. "Well, we'd have to change our fundamental understanding of the universe for that to be possible," Larsen says. A pause, and she grins. "Of course, that might well happen."